(A) Field of the Invention
The present invention is related to an antenna, more specifically, to a multi-band antenna.
(B) Description of Related Art
With the development of wireless communication, cellular phones and WLAN (Wireless Local Area Network) are becoming necessities for current communication. Various types and categories of antennas of WLAN apparatuses and cellular phones for signal receiving and transmitting are well developed in an attempt to cover wider radiation range, achieving better signal receiving and transmitting performance. Furthermore, antennas are designed to be smaller for portable requirement and installation space concern.
ISM (Industrial, Science and Medical) band is a free worldwide public band, of which the ranges are at frequency of 900 MHz, 2.4 GHz and 5 GHz. The range of 2.4 GHz RF (Radio Frequency) band is limited between 2.4-2.8435 GHz, which is overloaded at the present.
In order to achieve superior communication quality and stability, the new wireless communication protocol U-NII of 802.11a (47CFR15.401) additionally provides a band around 5 GHz for usage, in which the band of 5.150-5.250 GHz is used for radiation power below 50 mW, the band of 5.250-5.350 GHz is used for radiation power below 250 mW, and the band of 5.725-5.825 GHz is used for radiation power below 1000 mW. Communication protocol ISM of 802.11a (47CFR15.247) designates that 5.725-5.825 GHz is used for radiation power below 1000 mW. The above described wavelengths of wireless radio wave are between 51.30-58.25 mm. Furthermore, 802.11b/g ISM (47CFR15.247) designates that the band of 2.400-2.4835 GHz is used for radiation power below 1000 mV, and the wavelengths of wireless radio wave are between 120.7-125 mm.
Because widely used bands of 2.4 GHz and 5 GHz are not in double frequency resonant relation, if an antenna uses bands of 2.4 GHz and 5 GHz, the design is more difficult than that of a dual-band cellular phone using 900 MHz and 1800 MHz.
The object of the present invention is to provide a multi-band antenna, especially, for a WLAN apparatus, which occupies less space and has a capability of being used in various bands. By using multi-band antenna in current WLAN apparatuses, the WLAN apparatuses can be used in various bands regulated by different protocols without antenna change.
The multi-band antenna of the present invention comprises a dielectric plate, a first metal foil and two second metal foils, where the first metal foil and the second metal foils are adhered to a surface of the dielectric plate. The first metal foil comprises a first plate, a second plate, two first stripes and a connecting bar, the second plate including a first signal-fed point, the two first stripes being electrically connected to the first signal-fed point and symmetric along the second plate, the longitudinal direction of the first stripe being designated as a first direction. Each first stripe is spaced at a distance to the second plate, and the length of each first stripe is equivalent to one fourth wavelength of the first frequency used in the multi-band antenna. The connecting bar connects the centers of the facing sides of the first plate and the second plate. The longitudinal direction of the structure constituted of the first plate, the connecting bar and the second plate is along the first direction, and the total length of the first plate, the second plate and the connecting bar is equivalent to one fourth wavelength of the second frequency used in the multi-band antenna. The two second metal foils are symmetric along the first direction and are spaced according to the first metal foil along a second direction that is perpendicular to the first direction. Each second metal foil comprises a second stripe and a third stripe, where the second stripe may electrically connect to a second signal-fed point, whose longitudinal direction is in the first direction, and the length of the second stripe is equivalent to one fourth wavelength of the second frequency used in the multi-band antenna. The third stripe may electrically connect to the second signal-fed point, whose longitudinal direction is in the first direction, and the length of the third stripe is equivalent to one fourth wavelength of the first frequency used in the multi-band antenna.
For instance, the first frequency is within ISM 5 GHz band, and the second frequency is within ISM 2.4 GHz band.
The multi-band antenna can be installed in a notebook computer as a wireless signal receiving and transmitting apparatus. If an access point of a company uses ISM 2.4 GHz band, and that of another company uses ISM 5 GHz band, the multi-band antenna can be used to meet the different requirements of the different communication protocols for wireless network data transmission between these two companies.